loose Wires?????

I have a 77 280Z that I got about 6 months ago - I had a new alterantor put on, starter, and wires and plugs. She ran like a top for about 5 months. The trouble I am having with it is that I will be driving down the road with full power and all of a sudden it will cut off completely. With no sign or symptom. She just dies. And will not restart. The battery isnt loosing power, and you cant pop the clutch to start it either. Its just DEAD. When this happens I still have lights, but the radio will not work. Any clues as to what this may be. I have had her worked on 3 times now and everytime the mechanic tells me he has fixed the loose wire but everytime she quites on me. HELP!!!!